The present invention relates to a drill for generating a hole in a work piece, preferably a composite material comprising a shank having a substantially cylindrical envelope surface, and including a front longitudinal cutting end. The cutting end has two cutting portions arranged symmetrically about the center axis of the drill. The drill has a direction of rotation.
Known drills for drilling of composite material have a shape similar to drills for wood comprising a centering point and cutting edges arranged symmetrically therearound. The disadvantage with these drills is that they tear off the fibres being a part of the composite material, especially at the exit of the drill out of the material. The fibres are therefore forced outwardly at the exit such that the hole achieves a very fringy end and/or delamination in the surrounding fibre layer. Furthermore, the areas between the cutting tips and the centering point are filled up with cut material during drilling of stacks, i.e. drilling of sandwich materials, which disturbs the continuing drilling of the material. Furthermore, the center part of the drill cuts negatively, such that the matrix material, epoxi for example, melts and flows out of the hole wall and thereby impairs the strength of the hole area. The negative cutting incision of the center part of the drill furthermore results in that the drill requires a large feed force in order to penetrate the work material.
Another known drill is shown in U.S. Pat. No. 4,352,610. The drill is provided with brazed inserts having a large cutting angle such that the necessary power for the rotation of the drill is large. Furthermore, the drill is more complicated to produce relative to the drill according to the invention.
An object of the present invention is to provide a drill which may drill clean and fray-free holes.
Another object of the present invention is to provide a drill through which shape less power is needed for feed and rotation.
Still another object of the present invention is to provide a drill simple to manufacture.
Still another object is to provide a drill capable of drilling holes with small diameters.